A vitreous silica crucible is used during the manufacturing process of silicon single crystal by the Czochralski method. A polysilicon is put into the vitreous silica crucible and then is heated, so the highly purified polysilicon is melted and a silicon melt is obtained. While rotating a susceptor that holds the vitreous silica crucible, an end portion of a seed crystal is immersed into the silicon melt, and is pulled up while being rotated so as to produce the silicon single crystal. In order to keep the solid-liquid interface at the central part of the silicon melt's surface which allows the silicon melt to contact the silicon single crystal at approximately 1420° C. which is the melt point of silicon, the temperature of the vitreous silica crucible is controlled at a relatively high level with a range of 1450-1600° C. In a pulling-up process of the silicon single crystal which may last more than two weeks, sometimes the extent of sidewall sagging deformation at the rim portion of the vitreous silica crucible may be 5 cm and greater.
Silicon single crystal used as semiconductor material is produced by the Czochralski method, by which polysilicon is heated up to approximately 1450-1500° C. inside a vitreous silica crucible and then is pulled up. Because flash memory and DRAM are expected to rapidly have lower prices and higher performance, in order to meet such requirement, the diameter of the silicon single crystal is changing from 300 mmΦ which is mainly used currently to a larger size with a range of 400-450 mmΦ. In accordance with this situation, in order to produce silicon single crystal with a larger diameter, the diameter of a vitreous silica crucible's opening portion is also changing from 600 mm to a larger size of 1000 mm or more. As the diameter of the vitreous silica crucible's opening portion is becoming larger, accordingly the distance between the heater, which is disposed outside the vitreous silica crucible, and the center of the silicon single crystal is also becoming greater than before. For example, if the diameter of an opening portion is changed from 600 mm to 1000 mm, the distance between the heater and the center of the silicon single crystal will be 200 mm and greater. In addition, the quantity of the silicon melt at approximately 1450-1500° C. will also become larger along with increasing of the diameter of the vitreous silica crucible's opening portion. A crucible with a diameter of about 1000 mm has a weight of approximately 120 kg which is quite heavy for a person to move it by hand, and the weight of silicon melt contained in it is 900 kg and more. In other words, when the silicon single crystal is being pulled up, silicon melt with a temperature of around 1500° C. and a weight of 900 kg or more will be contained in the crucible.
As a result, the distance between the central axis of the susceptor and the rim area of the vitreous silica crucible will become greater. Therefore, a deviation between the central axis of the susceptor and the central axis of the vitreous silica crucible can no longer be ignored because problems start to occur in the pulling-up process of the singles crystal silicon. For example, when an angle is formed between the central axis of the susceptor and the vitreous silica crucible or a deviation appears between the parallel central axis of both of them, a turbulent flow will occur inside the silicon melt and then it will be more difficult to attach the seed crystal to the melt, resulting in a low single-crystal yield of silicon ingot.